Cases come in several "flavours ... " -
-Thin material - sleeve-like - just for the barest of scratch protection
-Neoprene sleeves. Same "envelope" nature of the above, but with a little "impact" protection
Many use the above to - and THEN plop the unit into a purse or briefcase. Or glove compartment.
Then there's "book-like" covers - where the eReader fits inbetween two "pages" of a leather or authentic-imitation-leather cover. Some have slots on the inside-left for business cards.
Problems with ALL of these is that when production costs are cut and they are offered for half of what we see on retails bookstore shelves, some use poor dyes. Some dye the interior portions where the eReader slides against, possibly transferring that dye color to your eReader's case/frame.
You indicate that you might want to also carry the charger in the same case. I would tend not to do that. Imagine your flat eReader in a briefcase or elsewhere, and the charger is in the same bag (in front of or in back of the eReader). Then s-q-u-e-e-z-e the bag - like the force it would receive during a little drop or accidental abuse. The force hitting the charger has the potential to breaking your screen: The eReader might get "bent" around it. Sounds outlandish - but it has happened. I'd rather protect my eReader with two "solid" pieces on either side of it, and have nothing else to potentially "press" against it.
What you USE regularly depends upon what (a) you like and (b) how you are transporting your eReader.
I fitted a DVD case that accommodates my eReader darned near perfectly. The resulting package is slim, sleek, smooth - I can easily carry it around anywhere. I also have a "leatherette book case" for it purchased off eBay. But it has those poor dyes, and actually adds enough weight/mass to the eReader to make it not as "attractive" to carry around.
So - for ME - a case that cost me nothing was the best case for how I travel around town. Second in line for ME would be my neoprene case.
Do you have a BestBuy or large bookstore nearby where you can actually "look and feel" some of the case options?
And please shy away from the "leather/leatherette" "bargains" on eBay and elsewhere. You can transfer dyes to your eReader with just normal, non-abusive everyday use.